The amplified detection of DNA is a continuous challenge in DNA bioanalysis. Different catalysts such as enzymes, catalytic nucleic acids (DNAzymes) or metal nanoparticles (NPs) were used for the amplified detection of DNA. Amplified DNA detection was accomplished by an autocatalytic and catabolic DNAzyme-mediated process. DNA sensing platforms of enhanced sensitivities were designed by the triggering of isothermal autonomous reactions that synthesize numerous DNAzyme units as a result of a single DNA-analyte recognition event. For example, by the design of a circular DNA scaffold, that consists of the replica sequence of the hemin/G-quadruplex, the recognition of the analyte-DNA triggered-on, in the presence of polymerase/dNTPs, the rolling circle amplification (RCA) that generated DNA nanochains of the hemin/G-quadruplex horseradish peroxidase (HRP)-mimicking DNAzyme that enabled the colorimetric or chemiluminescence detection of DNA. Also, by using two functional nucleic-acid-hairpin structures the recognition of the analyte-DNA by one of the DNA hairpins triggered-on the hybridization chain reaction (HCR) that led to DNAzyme chains consisting of the Mg2+-dependent DNAzyme or the hemin/G-quadruplex HRP-mimicking DNAzyme. A further approach for amplifying the DNA detection has included, the use of the Zn2+-dependent ligation DNAzyme, and the isothermal autonomous synthesis of the ligation DNAzyme units, as a result of the DNA recognition event. Also, DNA machineries consisting of a DNA template, on which the recognition of the target-DNA triggers-on, in the presence of polymerase/dNTPs and a nicking enzyme, the isothermal autonomous synthesis of the hemin/G-quadruplex HRP-mimicking DNAzyme or RNA-cleaving DNAzyme were reported as highly sensitive optical (fluorescent, colorimetric or chemiluminescence) sensing platforms.9 In contrast to the different amplifying schemes that involve the autonomous synthesis of catalytic labels as a result of the DNA sensing event, an alternative approach that includes the biocatalytic regeneration of the analyte was developed. For example, by using exonuclease III, Exo III, or endonucleases the recognition complexes were cleaved while regenerating the target-analyte for subsequent sensing events. A further goal in DNA sensing involves the multiplexed analysis of several targets. Semiconductor quantum dots (QDs) and micrometer-long metal barcode rods were applied for the multiplexed analysis of DNA using different readout mechanisms such as electrical, fluorescence, Raman spectroscopic fingerprints, fluorescence resonance energy transfer (FRET) and chemiluminescence resonance energy transfer (CRET) processes.
Similarly, the selective desorption of different probes labeled with different fluorophores from graphene oxide supports through the selective formation of probe/analyte duplexes was used for the multiplexed analysis of DNA.